You should be glad they fixed it really. The problem isn't Metro, the problem is that there was no trademark defence clauses in the Windows Store agreement at all. Here's the agreement, which for this post is version 3.0 dated 2012-07-09.

The wording in the guidance document that calls out "Metro" specifically will eventually be supported by vNext of that document which will be clearer about Microsoft's position of protecting partner trademarks. I suspect really what they want to do now is not end up with 33% of the apps in the Windows 8 store being called "Metro <Blah>", because that was happening.

A corollary point - I'm sure that if you happen to trade under the name Metro you'll be fine. Can you imagine MS turning round to Metro AG and telling them that they can't use that name in the store?

Update: Tom Warren just noticed that the wording in the guidance document has changed to remove the reference to "Metro". I still stand by what I say - expect explicit clarification of trademark rules in the next rev of those rules.